Pulldown Analysis for Progressive Collapse Assessment
Publication: Journal of Performance of Constructed Facilities
Volume 29, Issue 1
Abstract
A new nonlinear static alternate path analysis technique coined pulldown analysis is presented as an easy-to-implement alternative to the existing pushdown analysis for assessing the load redistribution capability of a building after a critical structural element has been suddenly removed. Unlike the pushdown analysis where gravity loads within the affected bays of a building are directly amplified, the pulldown analysis is associated with a downward force that is statically applied at the removed element location. This static pulldown force is equal in value to the axial compression force in the to-be-removed column of the intact frame multiplied by a dynamic increase factor (DIF), which aims to generate the best match of the peak dynamic responses of a damaged building through a nonlinear static analysis. A seismically designed nine-story steel moment frame is used as an example to illustrate the pulldown analysis procedure. Results from progressive collapse assessment of the example frame using the pulldown analysis and pushdown analysis are critically compared. It is found that the pulldown analysis is able to estimate the peak dynamic responses of the example frame with at least the same level of accuracy as those predicted by the pushdown analysis. Moreover, the pulldown analysis may lead to improved prediction of some important structural responses such as the peak axial forces in columns next to the removed column. Finally, to demonstrate how empirical DIF formulas for the pulldown analysis can be derived for practical applications, curve-fitting of data points, each consisting of the DIF and a parameter that approximately reflects the residual capacity level of the damaged frame under a given column removal scenario, is carried out for the example frame.
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Published In
Journal of Performance of Constructed Facilities
Volume 29 • Issue 1 • February 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Nov 8, 2012
Accepted: Mar 18, 2013
Published online: Mar 20, 2013
Discussion open until: Nov 5, 2014
Published in print: Feb 1, 2015
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